chore(deps): update dependency rack to '~>1.6.0' [security]

Author: renovate[bot]

example/animal-service/Gemfile

@@ -7,7 +7,7 @@ group :development, :test do
 end
 
 gem 'rake'
-gem 'rack', '~>1.5.2'
+gem 'rack', '~>1.6.0'
 gem 'json', '~>1.6'
 gem 'sqlite3'
 gem 'sequel'

example/zoo-app/Gemfile

@@ -7,6 +7,6 @@ group :development, :test do
 end
 
 gem 'rake'
-gem 'rack', '~>1.5.2'
+gem 'rack', '~>1.6.0'
 gem 'json', '~>1.6.8'
 gem 'httparty'